Method of preparing non-aging steels



2,771,651 METHOD OF PREPARING NON-AGING STEELS Eric R. Morgan,Dearbormand John C. Shync, Belleville, Mich assignors to Ford MotorCompany, Dearborn, Mich a corporation of Delaware 1 No Drawing.Application October 28, 1955,

- Serial No. 543,611

3 Claims. (Cl. 212-215 This invention is specifically directed to aprocess for the manufacture of rimmed chemically capped steel suitablefor the production of deep drawn parts. The specific virtue of thisprocess is that it enables steels of this type to be consistently andeconomically produced in a nonaging condition.

A large percentage of the sheet steel produced in this country ismanufactured by the classical rimming process described on page 444 ofFrancis and Camp entitled Making, Shaping and Treating 'of Steel. Asordinarily produced this steel is highly satisfactory for deep drawingoperations provided such operations are conducted U promptly after thesteel is given the final temper or skin pass. However, if this steel ispermitted to age appreciably as by storage for a few days at averagesummer temperatures it develops a yield point and increases in hardnessand loses ductility to a point-where commercially satisfactory deepdrawing operationsmay not be conducted. United States Letters. Patent2,356,450, issued August 22, 1944, to Epstein demonstrates anunderstanding of this problem and'suggests a solution by the addition ofsmall quantities of vanadium. The use of vanadium has been retarded byits scarcity, cost and general critical nature. A further solution hasbeen taught by Morgan and Shyne in copending application Serial No.497,462, filed March 28, '1955, and assigned to the assignee of thisinvention.

The present invention is predicated upon the use of the combination of aboron addition and chemical capping to give a very economical andcommercially dependable non-aging deep drawing steel.

In the execution of this invention a two hundred-ton "ice open hearthheat was prepared with the following analysis:

Percent Carbon 0.055 Manganese 0.27 Phosphorus 0.010 Sulphur 0.025Nickel 0.05 Chromium 0.01 Copper 0.05 Molybdenum 0.01 Tin 0.01

This heat was teemed into commercial thirteen ton ingot molds. Into oneof these ingots during teeming was added eight pounds of ferro-boroncontaining 17.5% boron. This addition was made as the metal was pouredinto the ingot mold. While boron is admittedly a deoxidizer, the amountadded in this instance was insutficient to do more than to slightlyinhibit the usual vigorous rimming action associated with this type ofmetal. This vigorous rimming action was allowed to proceed for two orthree minutes, or until a satisfactory skin had been built up on theexterior of the ingot. At this time the ingot was chemically capped bythe addition of aluminum as is customary in the steel industry. Thisaluminum addition took the form of three pounds of aluminum shot. Thetop of the ingot was thoroughly stirred after the addition of thealuminum. This treatment resulted in an ingot having a boron content of0.0045 This boron containing a chemically capped ingot was thenpermitted to solidify and take its normal course in its conversion intosheet steel.

A similar ingot was prepared except that 16 lbs. of 136% ferro-boron wasadded to the mold during the teeming of the thirteen ton ingot. Thisingot was permitted to rim and then was chemically capped with aluminum.The final analysis indicated a boron content of 0.0065

Chemical capping as used herein is defined in Basic Open Hearth SteelMaking, Revised Edition, 1951, pages 364, 3.65 and 369.

The physical properties obtained from these ingots are summarized in thefollowing tables:

Properties of ingot containing 0.0045 B Increase Ultimate Yield Total InYield Tensile Olsen I Rockwell Point Elonga- Condition Strength stren thCup 3" Elongation, Per- During (p s Test Hardness tion, Percent in 2Aging cen inches As Annealed 43, 200 8. 0 41. 4 Prestralned 10 o InTension and Ag 0 43, 470 0 42. 0 Temper Rolled 0.5" 399 40. 5 TemperRolled 0.5% and Aged 40. 9

1 Aged 7 days at room temperature. Aged 10 minutes in boiling water. ISheet thickness 0.036 inch.

Properties of mgot containing 0.0065 B Increase Ultimate Total In YieldTensile Olsen Rockwell Yield Point Elonga- Oonclltion Strength StrengthCup "13 Elongation,

I 1 During (p. s. i.) Test Hardness tion, Percent in Aging Percent 2Inches As Anneal 42, 660 7. 4 42. 1 Prestreined 10% lnTenslon and Aged 10 42, 700 0 43. 4 Temper Rolled 0.5% 398 39. o Temper Rolled 0.5% andged P 40. 0

Shoe

tthlok'nellmln Particular attention is invited to the factthatthe'standard boiling water aging treatment failed toappreciablyharden the metal.

The exact procedure for obtaining the requisite boron content in thesteel is immaterial as long as the rimming action is not detrimentallyaffected. For example, a portion of the boron may be added in the ladleif more economical. The total boron content carried in the metal leavingthe ladle should not substantially exceed 0.005 if proper rimming actionis to be had. The remainder of the boron should be added in the ingotafter the desired amount of rimming has taken place and while asubstantial portion of the steel is still molten. This boron should beadded prior to the addition of the aluminum so that the aluminum will beavailable to reduce back into the steel oxidized boron compounds in theslag floating on the molten portion of the ingot. However, if one iswilling to forego this matter of economy, the boron may be added afterthe aluminum as long as it actually alloys with the steel. The preferredpractice is to add a portion of the boron to the ingot mold as it isbeing teemed with molten metal, and to complete the addition of boron atthe time the ingot is chemically capped. Boron should be added to give aboron content in the steel of from 0.002% to 0.02% with a value of about0.008% preferred. The preferred range is 0.005% to 0.01% boron.

While aluminum is the preferred material for accomplishing the chemicalcapping, any strong deoxidizer not harmful to steel may be substitutedin its stead. For example, zirconium and titanium have been so employed.

Finished sheet steel from the boron treated ingot described in detailabove was stored for five weeks during the hottest part of the summerjust passed immediately adjacent to finished sheet steel from the sameheat which was not boron treated. The boron treated material whenpressed into automotive door panels made a product completelysatisfactory from every standpoint. The corresponding untreated metalwas quite unusable and had to be returned for roller leveling.

We claim as our invention:

1. The process of producing a rimmed steel which is substantiallynon-aging under usual conditions of commercial storage comprisingestablishing in a mold a mass of molten steel of rimming composition andhaving a boron content insufficient to detrimentally affect therimmingaction, permitting the rimming action to proceed until a skin hasbeen formed and after said skin has been formed chemically capping thesteel, said process being further characterized by the alloying of thesteel with sufiicient boron to yield a final boron content of 0.002% to0.02%.

2. The process of producing a rimmed steel which is substantiallynon-aging under usual conditions of commercial storage comprisingestablishing in a mold amass of molten steel of rimming composition andhaving a boron content insufficient to detrimentally affect the rim mingaction, permitting the rimming action to proceed until a skin has beenformed and after said skin has been formed chemically capping the steel,said process being further characterized by the alloying of the steelwith sufficient boron to yield a final boron content of 0.005% to 0.01%.

3. The process of producing a rimmed steel which is substantiallynon-aging under usual conditions of commercial storage comprisingestablishing in a mold a mass of molten steel of rimming composition andhaving a boron content insufiic'ient to detrimentally afiect the rimmingaction, permitting the rimming action to proceed until a skin has beenformed and after said skin has been formed chemically capping the steel,said process being further characterized by the alloying of the steelwith sufficient boron to yield a final boron content of about 0.008%.

1. THE PROCESS OF PRODUCING A RIMMED STEEL WHICH IS SUBSTANTIALLYNON-AGING UNDER USUAL CONDITIONS OF COMMERCIAL STORAGE COMPRISINGESTABLISHING IN A MOLD A MASS OF MOLTEN STEEL OF RIMMING COMPOSITION ANDHAVING A BORON CONTENT INSUFFICIENT TO DETRIMENTALLY AFFECT THE RIMMINGACTION, PERMITTING THE RIMMING ACTION TO PROCEED UNTIL A SKIN HAS BEENFORMED AND AFTER SAID SKIN HAS BEEN FORMED CHEMICALLY CAPPING THE STEEL,SAID PROCESS BEING FURTHER CHARACTERIZED BY THE ALLOYING OF THE STEELWITH SUFFICIENT BORON TO YIELD A FINAL BORON CONTENT OF 0.002% TO 0.02%.